This invention relates to the control of the delicate tissue paper web during its production and, more particularly, to the control of the conveyance of high bulk paper tissue of the type commonly used as facial and toilet tissue. Still more particularly, it relates to a pickup and drying arrangement for preserving and enhancing the high bulk properties, which are initially a part of a tissue web but which are usually lost or diminished during its passage through a papermaking machine, all the while controlling the conveyance of the web.
Illustrations of prior types of high bulk tissue, processes and machines for its manufacture are shown in U.S. Pat. Nos. 3,301,746 and 3,812,000. The apparatus disclosed in these patents for manufacturing such tissue have one common deficiency in their structural configurations. Specifically, at some point during the conveyance of the tissue web from its formation until it is removed from the last dryer, it is not carried by a felt, fabric or dryer roll surface. By "not carried," it is meant that the web, at some point along its path of travel, is either totally unsupported or must adhere to the bottom of the felt, fabric or dryer surface from which it can drop off or be temporarily separated from the felt, fabric or dryer surface. This is a situation which usually occurs between successive rolls along the web's serpentine path of travel in the papermaking machine.
Web support, and positive control of its movement, is important in the manufacture of all types of paper, but it is especially critical in the manufacture of tissue paper grades because of the comparatively high speeds involved (commonly about 3,000 fpm, but often up to about 4,000 fpm and, sometimes, over 5,000 fpm) and the relatively light weight of the tissue web itself (about 12-15 lbs. per 3,000 ft.sup.2). By contrast, a typical newsprint machine for example might run about 2,000 fpm with a web basis weight of about 32 lbs. per 3,000 ft.sup.2.
If the sheet is not supported and controlled during its manufacture, it might break or billow away from its carrier surface and become wrinkled as it passes through a roll nip or over a roll beneath the felt or fabric. Any such interruption in the papermaking process is very disruptive and expensive in terms of lost time. In addition, any wrinkled paper must be rejected and recycled.
The production of high bulk tissue is especially sensitive to web control since there is no press section in the papermachine configuration to compress the tissue web and thus tend to increase its stability and ease in handling.